Watermaker suddenly producing very little water

Problem

Our watermaker normally produces around 35–40 liters per hour. One morning it suddenly dropped to maybe 5–10 liters per hour. Pressure looked normal but the product water flow was very low. At first I thought the membrane was dying.

Fix

1. 1

   I checked the pre-filters and they looked a bit dirty but not terrible. I changed them anyway.

2. 2

   No improvement.

3. 3

   Then I noticed the seawater intake strainer. It was almost completely blocked with sea grass.

4. 4

   We had anchored in a shallow bay the night before.

5. 5

   After cleaning the strainer the flow immediately went back to normal.

6. 6

   Lesson learned: always check the intake first, not the expensive parts.